Can't install Mountain Lion, Macintosh HD is locked

Question

Hello All:
I'm having trouble installing ML.  The installer told me that my Macintosh HD had errors that could not be fixed.  I ran disk utility to verify/repair the HD.  It took a couple of tries / restarts.  I think I also reset the PRAM.  Now, I get to the point where I choose the disk for installation and it says that it's locked.  When I fire up the terminal and do a 'mount' I see that it's mounted up 'read-only' and I can't refresh the mount because it's the disk being used to boot.  How can I unlock the disk for the ML installer to continue?
Late 2008 Macbook Unibody.
Thanks
- Skylar

Answer 1

I had the disk lock error too and was stuck in Recovery Mode limbo with no way out except formatting my harddrive
For those of you who do not own any external harddrives or 8GB+ USB drives etc, this solution may be for you. Also, my machine is a macbook pro that had Lion (installed via App Store) and now has Mountain Lion (installed via App Store).
I do have a 4GB USB stick, so I used the terminal to copy some important files from my harddrive to my USB.
The command for that is  cp. Use cp -r for copying whole directories over.
$> cp -r /Volumes/Image\<push TAB key so it completes the name>/<file/directory> /Volumes/<USBDRIVE Name>/
Once I got the files I needed, I was ready to erase my harddrive *tear*
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So I rebooted my Macbook, held cmd+R (before the grey screen came on, until the apple logo appears).
  Then I was in Lion's Recovery Move (instead of Mountain Lion's Recovery mode
I used Disk Utility to try to erase my Mcintosh HD, but it complained that it can't do it. So I used the "Repair Option on it" then I fell asleep. You MUST let it finish! It may not seem like it will finish, but it will eventually say it cannot repair it.
When I came to (lol), It sais it could not repair my drive, but I tried the Erase option again, and it worked! (I used the "Fastest" setting, and my HD is Journaled, HFS+).
After it finished erasing, I rebooted, and instead of an Apple logo coming up at the boot screen, it showed a folder in it's place with a question mark. I freaked out at first but then I did this:
Use the power button to turn off your mac. Use it again to turn it on, and do the cmd+R trick, and this will put your computer in INTERNET RECOVERY MODE (I had never heard of this, but it saved my life). It takes about 30 minutes to do it's thing, then it will bring you to the Mountain Lion Recovery Mode again.
This time, when you click on Install OS X, it will bring up the Mountain Lion Install dialogue, and you should be able to select your HD with no problem. It will re-download the Mountain Lion install and takes about 6 hours. This is basically a clean install, instead of an upgrade.
Lesson of the day: BACKUP YOUR STUFF BEFORE YOU UPGRADE!
Let me know if this works for you, or doesn't work for you. I couldn't find any responses that helped me (as I did not have extra memory peripherals laying around), so I hope someone else finds it useful.